Bozena is definitely a Czech given name. It is derived from the Slavic word for God and literally means of God.
However, and that is a pretty wild guess, bozena, being an adjective, might have been used on a birth certificate to denote "a child of god". Something along the lines of in the year of God 1897, on the nth day of so-and-so month, God's child Helena Nemecek was born to parents so-and-so and his wife.... If that is the case, I would guess bozena is followed by your grandmother's first, middle and last name.
Having written that fiction-like paragraph, most likely your grandmother's name was Bozena, but she changed it to Helen when she came to the US.